Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as "spitting," with the waste ink being collected in a "spittoon" reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide faster, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solid content than the earlier dye based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper.
Early inkjet printers used a single monochromatic pen, typically carrying black ink. Later generations of inkjet printing mechanisms used a black pen which was interchangeable with a tri-color pen, typically one carrying the colors of cyan, magenta and yellow within a single cartridge. The tri-color pen was capable of printing a "process" or "composite" black image, by depositing a drop of cyan, a drop of magenta, and a drop of yellow ink all at the same location. Unfortunately, images printed with the composite black usually had rough edges, and the overall image, even the color portions, often had a non-black hue or cast, depending for instance, upon the type of paper used.
The next generation of printers further enhanced the images by using a dual pen system. These dual pen printers provided a black pen along with a tri-color pen, both of which were mounted in a single carriage. These dual pen devices had the ability to print crisp, clear black text while providing full color images. As another answer to the dissatisfaction with the composite black images, a quad pen printing mechanism was developed. These quad pen printers carried four cartridges in a single carriage. Quad pen plotters were also developed, some of which carried four cartridges, one in each of four carriages. These quad printing mechanisms had a first pen carrying black ink, a second pen carrying cyan ink, a third pen carrying magenta ink, and a fourth pen carrying yellow ink.
Unfortunately, both the quad pen printers and the dual pen printers produced images, such as photographic images, which had a "grainy" appearance. For example, when printing a light colored portion of an image, such as a flesh tone, yellow dots were printed and lightly interspersed with magenta dots. When viewed at a distance, these magenta dots provided a flesh tone appearance; however, upon closer inspection the magenta dots were quite visible, giving the image an undesirable grainy appearance. This grainy appearance was similar to the graininess seen in newspaper photographs, or in photos taken using the wrong speed ("ASA" or "ISO" rating) of photographic film in low light conditions.
Indeed, inkjet printing mechanisms are known as "binary drop devices" because they form images by either placing a drop of ink on the print medium or by not firing. Not firing a droplet leaves either the print medium, or a previously printed drop(s), exposed to view. Unfortunately, such binary drop devices give inherently grainy images due to the visual "step" between the "drop on" and "drop off" regions. Worse yet, the larger the drops printed, the more grainy the resulting image appears, whether printing color or gray-scale images.
These earlier inkjet printers provided crisp black text and bright vivid graphics and charts, yet they failed to provide images of near photographic type quality, such as portraits, scenic landscapes, and other natural appearing images. Other devices have been used to provide high quality images, such as continuous tone devices some of which use a dye sublimation processes. Unfortunately, these continuous tone devices are expensive, and very unlikely to be viable within the small office and home printer markets, which currently sell printers to consumers within the range of $200-$1,000 dollars.
Another printing system, known as an imaging printing system has been proposed. Using a basic dual pen printer, typically constructed for a monochrome (e.g. black) cartridge and a tri-color (e.g. cyan, magenta, yellow) cartridge, the monochrome cartridge is replaced with a tri-chamber "imaging cartridge." While the normally installed tri-color cartridge carries full colorant concentrations of inks, the imaging cartridge typically carries ink formulations having reduced colorant concentrations. For instance, the imaging cartridge may contain reduced colorant concentrations of cyan and magenta, and either a full or a reduced concentration of black ink. Of course, pens containing other color and concentration combinations may also be interchanged with the monochrome cartridge. For instance, two full color cartridges may be installed if extensive color graphics are being printed, such as for business charts. However, one true beauty of the imaging system is realized when the reduced colorant concentrations are used in the imaging cartridge in combination with a full color concentration cartridge. By interspersing droplets of reduced colorant concentration with droplets of the full colorant concentrations, the resulting images have a near photographic quality.
Unfortunately, in a dual pen inkjet printer, this ability to interchange the monochrome and multi-cartridges presents a unique set of problems when it comes to servicing of both types of cartridges. FIG. 13 is a sectional bottom view of a first prior art capping system, shown in cross section sealing the orifice plate of a multi-chamber tri-color pen P1, while FIG. 14 is a sectional rear elevational view taken along line 14--14 of FIG. 13. FIG. 15 is a sectional bottom view of a second prior art capping system, shown in cross section sealing the orifice plate of a monochrome black pen P2. FIG. 16 is a sectional rear elevational view taken along line 16--16 of FIG. 15. The color pen P1 has a silicon orifice or nozzle plate S1 that defines three sets of nozzles A, B and C (each aligned in a pair of linear nozzle arrays), as shown in FIG. 13. The black pen P2 has a silicon orifice or nozzle plate S2 that defines one set of nozzles D, aligned in two linear arrays, as shown in FIG. 15.
As shown in FIGS. 13-16, these previous designs have used two different methods of capping the color and black printheads, based on the printhead geometry. In these figures, the silicon nozzle plates S1, S2 are attached by encapsulant beads E to a portion of an electrical flex circuit F1 for pen P1, and flex circuit F2 for pen P2. The flex circuits F1, F2 deliver firing signals to energize the printhead resistors which are associated with each nozzle in sets A-C, D. An energized resistor heats the ink until a droplet is ejected from the nozzle associated with the energized resistor.
As can be seen in FIGS. 14 and 16, the encapsulant beads E project beyond the outer surface of the nozzle silicon S1, S2. In the past, separate caps have been used to seal the black pen P1 and the color pen P2, with each cap avoiding the encapsulant bead regions. FIGS. 13 and 14 show a prior art color cap G sealing along the outer surface of the flex circuit F1, surrounding both the silicon S1 and the encapsulant beads E. FIGS. 15 and 16 show a prior art black cap H surrounding the nozzles D, and sealed directly against the silicon S2, between the encapsulant beads E.
Unfortunately, these prior art cap designs G and H were not interchangeable. The black cap H could not seal the color pen P1 against the silicon S1 because there is not enough room between the nozzle groups A, B, C and the encapsulant beads E to seat the cap H. Conversely, the color cap G could not seal the black pen P2 around the exterior of the silicon S2 because toward an interconnect side I of pen P2, there is a hollowed-out or notched region N where there is no flex circuit or plastic with which to form a seal. In other words, for the black pen P2 the sealing surface along the interconnect side I ends abruptly almost at the edge of the silicon S2.
As a further complication to interchangeably sealing both the black and tri-chamber pens, their orifice plates differ in their distance, here in elevation, from the print media. For instance, a black pen may be on the order of 0.6 mm (millimeters) closer to the print media than a tri-color pen. These differences in pen-to-media spacing enhance the print quality but complicate the problem of trying to seal both pens with the same cap. Using a conventional cap, such as G or H, to seal the color pen (farthest from the media) with an adequate force would result in too great a force when the same cap was used to seal the black pen. Sealing the black pen with such a great force may cause the elastomeric cap lips to buckle and perhaps to take a permanent set, which would then fail to seal a color pen when installed. Conversely, using the correct capping force for the black pen (closest to the media), would result in a cap would not even touch the color pen when installed.
One other earlier capping system, is currently commercially available in the DeskJet.RTM. 850C and DeskJet.RTM. 855C model color inkjet printers, sold by the Hewlett-Packard Company of Palo Alto, Calif. The black and tri-color cartridges used in these printers have a different design than the cartridges illustrated herein, so different challenges were encountered in designing suitable capping systems. The capping system in these earlier printers used a multiple sealing lip system to seal along the length of (parallel to) the encapsulant beads, not across (perpendicular to) the beads which is the challenge faced here. That is, in this earlier design the multiple sealing lips were parallel to the encapsulant beads to accommodate for manufacturing tolerance accumulation, so at least one of the multiple lips would land in a suitable location on the silicon to form a seal.
To solve the dilemma of sealing two different style printheads, of course two different caps could be installed in a service station, one for accommodating each type of pen when installed in the printer. However, such a two cap system is cumbersome, requiring extra physical space within the printer, which leads to a larger product that many consumers find undesirable. Moreover, such a two cap system, one for accommodating each type of pen, unfortunately increases the cost of the resultant printer, by requiring extra parts and assembly steps. Thus, it is desirable to have a universal capping system which is capable of sealing both monochrome and multi-chamber printheads.